Cyclosporin derivatives of the present invention are disclosed which possess enhanced efficacy and reduced toxicity over naturally occurring and other presently known cyclosporins and cyclosporine derivatives. The cyclosporin derivatives of the present invention are produced by chemical and isotopic substitution of the cyclosporine A (CsA) molecule by:                1. Chemical substitution and optionally deuterium substitution of amino acid 1; and        2. Deuterium substitution at key sites of metabolism of the cyclosporine A molecule such as amino acids 1, 4, 9.        
The cyclosporins are a family of, neutral, hydrophobic cyclic undecapeptides, containing a novel nine-carbon amino acid (MeBmt) at position 1 of the ring that exhibit potent immunosuppressive, antiparasitic, fungicidal, and chronic anti-inflammatory properties. The naturally occurring members of this family of structurally related compounds are produced by various fungi imperfecti. Cyclosporines A and C, are the major components. Cyclosporine A, which is discussed further below, is a particularly important member of the cyclosporin family of compounds. Twenty four minor metabolites, also oligopeptides, have been identified: Lawen et al, J. Antibiotics 42, 1283 (1989); Traber et al, Helv. Chim. Acta 70, 13 (1987); Von Wartburg and Traber Prog. Med. Chem., 25, 1 (1988).
Isolation of cyclosporines A and C, as well as the structure of A were reported by A. Ruegger et al., Helv. Chim. Acta 59, 1075 (1976); M. Dreyfuss et al., J. Appl. Microbiol. 3, 125 (1976). Crystal and molecular structures of the iodo derivative of A have been reported by T. J. Petcher et al., Helv. Chim. Acta 59, 1480 (1976). The structure of C was reported by R. Traber et al., ibid. 60, 1247 (1977). Production of A and C has been reported by E. Harri et al., U.S. Pat. No. 4,117,118 (1978 to Sandoz). Isolation, characterization and antifungal activity of B, D, E, as well as the structures of A through D have been reported by R. Traber et al., Helv. Chim. Acta 60, 1568 (1977). Isolation and structures of E, F, G, H, I: eidem, ibid. 65, 1655 (1982). Preparation of [2-Deutero-3-fluoro-D-Ala]8-CsA is disclosed by Patchett et al in GB 2,206,199A which was published on Dec. 29, 1988.
Cyclosporin was discovered to be immunosuppressive when it was observed to suppress antibody production in mice during the screening of fungal extracts. Specifically, its suppressive effects appear to be related to the inhibition of T-cell receptor-mediated activation events. It accomplishes this by interrupting calcium dependent signal transduction during T-cell activation by inactivating calmodulin and cyclophilin, a peptidyl propyl isomerase. It also inhibits lymphokine production by T-helper cells in vitro and arrests the development of mature CD8 and CD4 cells in the thymus. Other in vitro properties include inhibition of IL-2 producing T-lymphocytes and cytotoxic T-lymphocytes, inhibition of IL-2 released by activated T-cells, inhibition of resting T-lymphocytes in response to alloantigen and exogenous lymphokine, inhibition of IL-1 production, and inhibition of mitogen activation of IL-2 producing T-lymphocytes. Further evidence indicates that the above effects involve the T-lymphocytes at the activation and maturation stages.
Stimulation of TCR (T cell receptor) by foreign antigen on a major histocompatibility (MHC) molecule on the surface of the T cell results in the activation of a TCR signal transmission pathway (exact method of transmission unknown) through the cytoplasm causing the signal results in the activation of nuclear transcription factors, i.e. nuclear factors of activated T-cells (NF-AT) which regulate transcription of T-cell activation genes. These genes include that of lymphokine interleukin-2 (IL-2). Translation of the message is followed by secretion of IL-2. T-cell activation also involves the appearance of the lymphokine receptor IL-2R on the cell surface. After IL-2 binds to IL-2R, a lymphokine receptor (LKR) signal transmission pathway is activated. The immunosuppressive drug, rapamycin, inhibits this pathway.
CsA is a potent inhibitor of TCR-mediated signal transduction pathway. It inhibits binding of NF-AT to the IL-2 enhancer, and thus inhibits transcriptional activation. CsA binds to cyclophilin, which binds to calcineurin, which is a key enzyme in the T-cell signal transduction cascade.
Cyclophilin is found in prokaryotic and eukarotic organisms and is ubiquitous and abundant. Cyclophilin is a single polypeptide chain with 165 amino acid residues. It has a molecular mass of 17.8 kD. A roughly spherical molecule with a radius of 17 angstroms, cyclophilin has an eight-stranded antiparallel beta barrel. Inside the barrel, the tightly packed core contains mostly hydrophobic side chains. CsA has numerous hydrophobic side chains which allow it to fit into the cyclophilin beta barrel. Cyclophillin catalyzes the interconversion of the cis and trans-rotamers of the peGIFdyl-prolyl amide bond of peptide and protein substrates. Cyclophilin is identical in structure with peptidyl prolyl cis-trans isomerase and bears structural resemblance to the superfamily of proteins that transports ligands such as retinol-binding protein (RBP). These proteins carry the ligand in the barrel core. But cyclophilin actually carries the ligand binding site on the outside of the barrel. The tetrapeptide ligand binds in a long deep groove on the protein surface between one face of the beta barrel and the Thr116-Gly130 loop.
Further properties have also been reported in studies of the biological activity of CsA: J. F. Borel et al., Agents Actions 6, 468 (1976). Pharmacology: Eidem. Immunology 32, 1017 (1977); R. Y. Calne, Clin. Exp. Immunol. 35, 1 (1979). Human studies: R. Y. Calne et al., Lancet 2, 1323 (1978); R. L. Powles et al., ibid. 1327; R. L. Powles et al., ibid 1, 327 (1980). In vitro activity (porcine T-cells): D. J. White et al., Transplantation 27, 55 (1979). Effects on human lymphoid and myeloid cells: M. Y. Gordon, J. W. Singer, Nature 279, 433 (1979). Clinical study of CsA in graft-versus-host disease: P. J. Tutschka et al., Blood 61, 318 (1983).
Mechanism of Cyclosporine A Action
Cyclosporine A-Cyclophilin A Complex
CsA, as discussed above, binds to the cyclophilin beta barrel. Thirteen CyP A residues define the CsA binding site. These residues are Arg 55, Phe 60, Met 61, Gln 63, Gly 72, Ala 101, Asn 102, Ala 103, Gln 111, Phe 113, Trp 121, Leu 122, His 126. The largest side-chain movements are 1.3 A for Arg 55 and up to 0.7 A for Phe 60, Gln 63, and Trp 121. There are four direct hydrogen bonds between the CyP A and CsA. Residues 4, 5, 6, 7, 8 of CsA protrude out into the solvent and are thought to be involved in binding the effector protein, calcineurin (Pflugl, G., Kallen, J., Schirmer, T., Jansonius, J. N., Zurini, M. G. M., & Walkinshaw, M. D. (1993) Nature 361, 91-94.)
Function of CsA-CyP A Complex
The CsA-CyP A complex inhibits the phosphatase activity of the heterodimeric protein serine/threonine phosphatase or calcineurin (Liu, J., Farmer, J. D., Lane, W. S., Friedman, J., Weissman, I., & Schreiber, S. L. (1991) Cell 66, 807-15; Swanson, S. K., Born, T., Zydowsky, C. D., Cho, H., Chang, H. Y., & Walsh, C. T. (1992) Proc. Natl. Acad. Sci. USA 89, 3686-90). CyP A binds CsA with an affinity of ca. 10 nM. The complex is then presented to calcineurin (Liu, J., Farmer, J. D., Lane, W. S., Friedman, J., Weissman, I., & Schreiber, S. L. (1991) Cell 66, 807-15.).
Calcineurin dephosphorylates the transcription factor NFAT found in the cytoplasm of T-cells. Dephosphorylation allows NFAT to translocate to the nucleus, combine with jun/fos genes and activate the transcription of the IL-2 gene responsible for cell cycle progression, leading to immune response. CsA-CyP A complex inhibits the phosphatase activity of calcineurin and ultimately immunosuppression (Etzkorn, F. A., Chang, Z., Stolz, L. A., & Walsh, C. T. (1994) Biochemistry 33, 2380-2388.). Neither CsA or CyP A alone are important immunologically. Only their complex is important (Liu, J., Farmer, J. D., Lane, W. S., Friedman, J., Weissman, I., & Schreiber, S. L. (1991) Cell 66, 807-15).
Metabolism of Cyclosporine:
Cyclosporine is metabolized in liver, small intestine and kidney to more than 30 metabolites. The structure of 13 metabolites and 2 phase II metabolites have been identified and at least 23 further metabolites have been isolated by HPLC and their structures characterized by mass spectrometry. The reactions involved in phase I metabolism of cyclosporine are hydroxylation, demethylation as well as oxidation and cyclisation at amino acid 1. Several clinical studies and reports showed an association between blood concentrations of cyclosporine metabolites and neuro- or nephrotoxicity. In vitro experiments indicate that metabolites are considerably less immunosupressive and more toxic than CsA.
As exemplified by the ever expanding list of indications for which CsA has been found useful, the cyclosporin family of compounds find utility in the prevention of rejection or organ and bone marrow transplants; and in the treatment of psoriasis, and a number of autoimmune disorders such as type 1 diabetes mellitus, multiple sclerosis, autoimmune uveitis, and rheumatoid arthritis. Additional indications are discussed infra.
As is generally accepted by those of skill in the art, inhibition of secretion of interleukin-2 (IL-2) and other lymphokines from lymphocytes, is a useful indicator of intrinsic immunosuppressive activity of a cyclosporin analog. For a recent review of cyclosporin uses and mechanisms of action see Wenger et al Cyclosporine: Chemistry, Structure-Activity Relationships and Mode of Action, Progress in Clinical Biochemistry and Medicine, vol. 2, 176 (1986).
Cyclosporin A is a cyclic peptide which contains several N-methyl amino acids and, at position-8, contains a D-alanine. The structure of Cyclosporin Aa is given below: aUnless otherwise specified, each of the amino acids of the disclosed cyclosporin is of the L-configuration.

As is the practice in the field, a particular cyclosporin analog may be named using a shorthand notation identifying how the analog differs from cyclosporin A. Thus, cyclosporin C which differs from cyclosporin A by the threonine at position-2 may be identified as [Thr]2-cyclosporin or [Thr]2-CsA. Similarly, cyclosporin B is [Ala]2-CsA; cyclosporin D is [Val]2-CsA; cyclosporin E is [Val]11-CsA; cyclosporin F is [3-DesoxyMeBmt]1-CsA; cyclosporin G is [NVa]2-CsA; and cyclosporin H is [D-MeVal]11-CsA.
D-Serine and D-Threonine have been introduced into the 8-position of cyclosporin A by biosynthesis resulting in active compounds. See R. Traber et al. J. Antibiotics 42, 591 (1989). D-Chloroalanine has also been introduced into position-8 of Cyclosporin A by biosynthesis. See A. Lawen et al J. Antibiotics 52, 1283 (1989).
Indications for Cyclosporine Therapy
Immunoregulatory abnormalities have been shown to exist in a wide variety of autoimmune and chronic inflammatory diseases, including systemic lupus erythematosis, chronic rheumatoid arthritis, type 1 diabetes mellitus, inflammatory bowel disease, biliary cirrhosis, uveitis, multiple sclerosis and other disorders such as Crohn's disease, ulcerative colitis, bullous pemphigoid, sarcoidosis, psoriasis, ichthyosis, and Graves opthalmopathy. Although the underlying pathogenesis of each of these conditions may be quite different, they have in common the appearance of a variety of autoantibodies and self-reactive lymphocytes. Such self-reactivity may be due, in part, to a loss of the homeostatic controls under which the normal immune system operates.
Similarly, following a bone marrow or an organ transplantation, the host lymphocytes recognize the foreign tissue antigens and begin to produce antibodies which lead to graft rejection.
One end result of an autoimmune or a rejection process is tissue destruction caused by inflammatory cells and the mediators they release. Anti-inflammatory agents, such as NSAID's (Non-Steroidal Anti-inflammatory Drugs), and corticosteroids act principally by blocking the effect of, or secretion of, these mediators, but do nothing to modify the immunologic basis of the disease. On the other hand, cytotoxic agents, such as cyclophosphamide, act in such a nonspecific fashion that both the normal and autoimmune responses are shut off. Indeed, patients treated with such nonspecific immunosuppressive agents are as likely to succumb to infection as they are to their autoimmune disease.
Generally, a cyclosporin, such as cyclosporine A, is not cytotoxic nor myelotoxic. It does not inhibit migration of monocytes nor does it inhibit granulocytes and macrophage action. Its action is specific and leaves most established immune responses intact. However, it is nephrotoxic and is known to cause the following undesirable side effects:
(1) abnormal liver function;
(2) hirsutism;
(3) gum hypertrophy;
(4) tremor;
(5) neurotoxicity;
(6) hyperaesthesia; and
(7) gastrointestinal discomfort.
A number of cyclosporines and analogs have been described in the patent literature:    U.S. Pat. No. 4,108,985 issued to Ruegger, et al. on Aug. 22, 1978 entitled, “Dihydrocyclosporin C”, discloses dihydrocyclosporin C, which can be produced by hydrogenation of cyclosporin C.    U.S. Pat. No. 4,117,118 issued to Harri, et al. on Sep. 26, 1978 entitled, “Organic Compounds”, discloses cyclosporins A and B, and the production thereof by fermentation.    U.S. Pat. No. 4,210,581 issued to Ruegger, et al. on Jul. 1, 1980 entitled, “Organic Compounds”, discloses cyclosporin C and dihydrocyclosporin C which can be produced by hydrogenation of cyclosporin C.    U.S. Pat. No. 4,220,641, issued to Traber, et al. on Sep. 2, 1980 entitled, “Organic Compounds”, discloses cyclosporin D, dihydrocyclosporin D, and isocyclosporin D.    U.S. Pat. No. 4,288,431 issued to Traber, et al. on Sep. 8, 1981 entitled, “Cyclosporin Derivatives, Their Production and Pharmaceutical Compositions Containing Them”, discloses cyclosporin G, dihydrocylosporin G, and isocyclosporin G.    U.S. Pat. No. 4,289,851, issued to Traber, et al. on Sep. 15, 1981 entitled, “Process for Producing Cyclosporin Derivatives”, discloses cyclosporin D, dihydrocyclosporin D, and isocyclosporin D, and a process for producing same.    U.S. Pat. No. 4,384,996, issued to Bollinger, et al. on May 24, 1983 entitled “Novel Cyclosporins”, discloses cyclosporins having a β-vinylene-α-amino acid residue at the 2-position and/or a β-hydroxy-α-amino acid residue at the 8-position. The cyclosporins disclosed included either MeBmt or dihydro-MeBmt at the 1-position.    U.S. Pat. No. 4,396,542, issued to Wenger on Aug. 2, 1983 entitled, “Method for the Total Synthesis of Cyclosporins, Novel Cyclosporins and Novel Intermediates and Methods for their Production”, discloses the synthesis of cyclosporins, wherein the residue at the 1-position is either MeBmt, dihydro-MeBmt, and protected intermediates.    U.S. Pat. No. 4,639,434, issued to Wenger, et al on Jan. 27, 1987, entitled “Novel Cyclosporins”, discloses cyclosporins with substituted residues at positions 1, 2, 5 and 8.    U.S. Pat. No. 4,681,754, issued to Siegel on Jul. 21, 1987 entitled, “Counteracting Cyclosporin Organ Toxicity”, discloses methods of use of cyclosporin comprising co-dergocrine.    U.S. Pat. No. 4,703,033 issued to Seebach on Oct. 27, 1987 entitled, “Novel Cyclosporins”, discloses cyclosporins with substituted residues at positions 1, 2 and 3. The substitutions at position-3 include halogen.    H. Kobel and R Traber, Directed Biosynthesis of Cyclosporins, European J. Appln. Microbiol. Biotechnol., 14, 237B240 (1982), discloses the biosynthesis of cyclosporins A, B, C, D & G by fermentation.    Additional cyclosporin analogs are disclosed in U.S. Pat. No. 4,798,823, issued to Witzel, entitled, New Cyclosporin Analogs with Modified “C-9 amino acids”, which discloses cyclosporin analogs with sulfur-containing amino acids at position-1.